Astrobiology Top 10: Dawn Rising

The Dawn mission to study Vesta and the dwarf planet Ceres in the asteroid belt launched September 27 at 7:34 am Eastern Daylight Time. The four-year, 1.8 billion-mile flight started with the rumble and roar of a Delta II rocket that hurtled the Dawn spacecraft off a launch pad in Florida and into space.

Launch of the Dawn mission to study Vesta and Ceres in the asteroid belt. Image Credit: NASA

Launch controllers at Cape Canaveral Air Force Station monitored a near-perfect countdown leading to launch, and then applauded as the rocket’s three stages performed perfectly in dispatching Dawn on its way.

Dawn spread its solar panel "wings" after reaching orbit. It will depend on a modestly powered set of ion engines to maneuver itself around Earth and Mars on its way to Vesta and Ceres. These two asteroid belt behemoths have been witness to much of our solar system’s history.

"Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts," said Dawn Principal Investigator Christopher Russell of the University of California, Los Angeles. "One is rocky and is representative of the building blocks that constructed the planets of the inner solar system. The other may very well be icy and represents the outer planets. Yet, these two very diverse bodies reside in essentially the same neighborhood. It is one of the mysteries Dawn hopes to solve."

Using the same spacecraft to reconnoiter two different celestial targets makes both fiscal and scientific sense. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn’s science instrument suite will measure mass, shape, surface topography and tectonic history, elemental and mineral composition, as well as seek out water-bearing minerals. In addition, the Dawn spacecraft itself and the way it orbits both Vesta and Ceres will be used to measure the celestial bodies’ gravity fields.

NASA’s Dawn mission will visit two of the first bodies formed in our solar system: the "dwarf planet" Ceres and the massive asteroid Vesta.Image Credit: NASA

"Understanding conditions that lead to the formation of planets is a goal of NASA’s mission of exploration," said David Lindstrom, Dawn program scientist at NASA Headquarters, Washington. "The science returned from Vesta and Ceres could unlock many of the mysteries of the formation of the rocky planets including Earth."

Before all this celestial mystery unlocking can occur, Dawn has to reach the asteroid belt and its first target – Vesta. This is a four-year process that begins with launch and continues with the firing of three of the most efficient engines in NASA’s space motor inventory – ion propulsion engines. Employing a complex commingling of solar-derived electric power and xenon gas, these frugal powerhouses must fire for months at a time to propel as well as steer Dawn. Over their eight-year, almost 4-billion-mile lifetime, these three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) – a record for spacecraft.

To cruise from Earth to its targets, the spacecraft will travel in a long outward spiral. In February 2009 the spacecraft will swing by the planet Mars for a gravity assist. Dawn should reach the asteroid Vesta in September 2011, and remain in orbit around the asteroid until April of 2012. Then the spacecraft will head for Ceres, and should arrive there in February 2015.

UPDATE: On December 18, 2007, Dawn successfully completed the initial checkout phase of the mission. The spacecraft has now begun its interplanetary cruise phase.